package com.leon.base;
import java.util.Iterator;

public class ResizingArrayStack<Item> implements Iterable<Item> {
    private Item[] a;
    private int N;


    private class ReverseArrayIterator implements Iterator<Item>
    {
        private int i = N;
        @Override
        public boolean hasNext() {
            return i > 0 ;
        }

        @Override
        public Item next() {
            return a[--i];
        }

        @Override
        public void remove() {

        }
    }

    @Override
    public Iterator<Item> iterator() {
        return new ReverseArrayIterator();
    }

    public ResizingArrayStack() {
        a = (Item[]) new Object[1];
        N = 0;
    }
    public void push(Item item){
        if(N==a.length) resize(2*a.length);
        a[N++] = item;
    }
    public Item pop()
    {
        Item item = a[--N];
        a[N] = null;
        if(N>0 && N == a.length/4) resize(a.length/2);
        return item;
    }
    public boolean isEmpty()
    {
        return N==0;
    }
    public int size()
    {
        return N;
    }
    private void resize(int max)
    {
        Item[] temp = (Item[]) new Object[max];
        for (int i = 0; i < N; i++) {
            temp[i] = a[i];
        }
        a = temp;
    }
}
